【Objective】 To explore the effects of exogenous CaCl2 on the growth and photosynthetic characteristics of marigold under saline-alkali stress, and to provide theoretical support for the application of CaCl2 to improve the cultivation efficiency and product quality of marigold on saline-alkali land.【Methods】 Taking Tagetes erecta L.seedlings as test materials, pot experiment was carried out to observe the growth phenotype, photosynthetic pigment content, photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of Tagetes erecta L.seedlings by watering (CK1), root irrigation with 80 mmol / L mixed saline-alkali solution ( NaCl∶NaHCO3 = 1∶1, CK2 ) and root irrigation with saline-alkali followed by foliar spraying with four concentrations of CaCl2 solution [ 5,10,15,20 mmol/L ].【Results】With the prolongation of saline-alkali stress time, the plant height, stem diameter, root configuration and root-shoot ratio of marigold plants showed a gradual upward trend, and the net photosynthetic rate ( Pn ), transpiration coefficient ( Tr ), stomatal conductance ( Gs ), chlorophyll a content ( Chl a ), chlorophyll b content ( Chl b ), total chlorophyll content ( Chl t ), initial fluorescence ( F0 ), maximum fluorescence ( Fm ) and maximum photochemical efficiency ( Fv/Fm ) of leaves showed a downward trend, while intercellular CO2 concentration ( Ci ) showed an upward trend. After spraying different concentrations of CaCl2 on the leaves, the change range of each index decreased. There was a concentration effect, and the effect of 10 mmol / L CaCl2 treatment was the best. On the 20 th day of stress, the Chl a, Chl b, Chl t, Pn, Tr, Gs, F0, Fm and Fv / Fm of leaves treated with 10 mmol / L CaCl2 were significantly higher than those of CK2 by 52.39 %, 48.51 %, 46.78 %, 45.53 %, 49.51 %, 49.57 %, 31.60 %, 43.80 % and 32.83 %, respectively. The root-shoot ratio and Ci were significantly reduced by 22.60 % and 30.91 %, respectively.【Conclusion】 Spraying 10 mmol/L CaCl2 on the leaves could significantly reduce the decrease of chlorophyll synthesis precursors in marigold leaves under saline-alkali stress, increase the electron transport rate of PSII, enhance the photosynthetic capacity of leaves, and effectively improve the growth of plants.